Various compositions have been used to aid in the conduction of heat from one surface to another surface. For example, in electrical devices it is important to conduct heat from circuit boards and components to a metal plate or cooling device which can then remove the heat from the electrical device. Elastomeric compositions have been used which contain various additives and fillers which increase the thermal conductivity of the elastomers. Such elastomers are illustrated in U.S. Pat. No. 4,604,424 to Cole et al. Thermally conductive elastomers which typically have a Shore A durometer hardness in the range of about 50 are relatively hard and lack the sufficient conformability to easily conform to irregular shaped substrates, such as printed circuit boards containing transistors, resistors, diodes and other electrical components thereon. Such conductive elastomers require high pressure compression, typically in the range of 300 psi to 500 psi, to assure the desired contact with the substrate from which or to which heat is being conducted. Therefore, such elastomers are typically not suited for direct contact with electronic components for aiding in the removal of heat.
Various grease materials and pastes have been prepared using similar thermally conductive fillers. However, such greases and pastes have the disadvantages of migrating into unwanted areas over time, particularly at elevated temperatures, thus contaminating other areas of the device and causing a loss of the desired thermal conductivity, and of being very difficult to handle when reentering the electrical device for repair or replacement. This is due to the fact that the grease or paste is difficult to clean from the surfaces on which it has been placed.
In some instances the thermal conductivity of thermally conductive elastomers have been enhanced by using a thermally conductive grease to aid in the surface contact of the elastomer with the substrate. Other interface materials have been used as well. As with using a grease the disadvantage of such interface materials is that it is difficult to clean such materials from the substrate such as an electronic device when reentry and removal of the conductive elastomer is necessary for repair or replacement.